ML23017A151
| ML23017A151 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 01/10/2023 |
| From: | Benjamin Beasley NRC/NRR/DANU/UAL1 |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| Download: ML23017A151 (1) | |
Text
8 ELECTRICAL POWER SYSTEMS THIS NRC STAFF DRAFT SE HAS BEEN PREPARED AND IS BEING RELEASED TO SUPPORT INTERACTIONS WITH THE ACRS. THIS DRAFT SE HAS NOT BEEN SUBJECT TO FULL NRC MANAGEMENT AND LEGAL REVIEWS AND APPROVALS, AND ITS CONTENTS SHOULD NOT BE INTERPRETED AS OFFICIAL AGENCY POSITIONS.
This chapter of the Hermes construction permit safety evaluation report (SER) describes the technical review and evaluation by the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) of the preliminary design of the Kairos Power LLC (Kairos) Hermes Non-Power Reactor facility as presented in Chapter 8, Electric Power Systems, of the Hermes preliminary safety analysis report (PSAR) and supplemented by Kairos letter dated June 20, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22171A015). The staff reviewed Hermes PSAR Chapter 8 against applicable regulatory requirements using regulatory guidance and standards to assess the sufficiency of the preliminary design of the Hermes facility. The following sections of the SER describe the areas reviewed as specified in NUREG-1537, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Part 2, Standard Review Plan and Acceptance Criteria (ADAMS Accession No. ML042430048).
8.1 Electrical Systems Hermes PSAR Section 8.1, Summary Description, states that the purpose of the electrical system is to provide power to plant equipment for operation and that the electrical system consists of the non-Class 1E normal power system and the backup power system. Further, Kairos states that, due to the passive design of Hermes, safety-related structures, systems, and components (SSCs) do not require electric power to perform safety-related functions following a design basis event. The design has no emergency electrical power systems as described in NUREG-1537, Part 2, Section 8.2. In addition, Kairos states that alternating current (AC) power from off-site or backup power sources is not required to mitigate a design basis event.
8.2 Normal Power System Introduction Hermes PSAR Section 8.2, Normal Power System, states that the normal power system is supplied by an offsite power source from the local utility, which provides a medium voltage feeder. Further, Kairos states that the nominal bus voltage of 480 volts (V) is distributed to plant loads and a loss of voltage or a degraded voltage condition on the normal power system does not adversely affect the performance of safety-related functions.
Regulatory Evaluation The applicable regulatory requirements for the evaluation of Hermes are as follows:
10 CFR 50.34, Contents of applications; technical information, paragraph (a), Preliminary safety analysis report, including:
o 10 CFR 50.34(a)(3), which requires The preliminary design of the facility including: (i) The principal design criteria for the facility and (ii) The design bases and the relation of the design bases to the principal design criteria.
o 10 CFR 50.34(a)(4), which requires [a] preliminary analysis and evaluation of the design and performance of structures, systems, and components [SSCs] of the facility; and 10 CFR 50.35, Issuance of construction permits.
10 CFR 50.40, Common standards.
NUREG-1537, Part 2, Section 8.1, Normal Electrical Power Systems, states that the acceptance criteria for normal electrical power systems are:
The design and functional characteristics should be commensurate with the design bases, which are derived from other chapters of the PSAR.
The facility should have a dedicated substation, or a shared system designed to provide reasonable assurance that other uses could not prevent safe reactor shutdown.
The system should be designed to permit safe reactor shutdown and to prevent uncontrolled release of radioactive material if offsite power is interrupted or lost. Reactor shutdown is generally achieved by a reactor scram.
Electrical power circuits should be isolated sufficiently to avoid electromagnetic interference with safety-related instrumentation and control functions.
Technical specifications should be provided to ensure operability commensurate with power requirements for reactor shutdown and to prevent uncontrolled release of radioactive material.
The Principal Design Criteria (PDC) for the facility SSCs are described in Hermes PSAR Section 3.1 and are based on those specified in the NRC-approved Kairos Power Topical Report, KP-TR-003-NP-A, Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled, High Temperature Reactor (ADAMS Accession No. ML20167A174). Hermes PSAR, Section 3.1, Table 3.1-3, Principal Design Criteria identifies PDC 17 and 18 as applicable to Chapter 8.
Technical Evaluation The normal power system provides AC and direct current (DC) electrical power by an offsite power source and is designed in accordance with National Fire Protection Association (NFPA) 70, National Electrical Code 2020, as stated in PSAR Section 8.2.3, System Evaluation.
In PSAR Section 8.2.1.1, AC Electrical Power, Kairos states that AC electrical power components include the following:
A single incoming feeder from the utility to the normal power system with nominal feeder voltage of 4.16 kilovolt (kV),
A 4.16 kV/480 V step down transformer, and The low voltage AC electrical power distribution with nominal bus voltages of 480 V and 120 V.
Further, Kairos stated that selected loads are supplied continual AC power via uninterruptible power supplies (UPS), which provides power during normal operations and backup power during loss of normal electrical power.
In PSAR Section 8.2.1.2, DC Electrical Power, Kairos states that 24 VDC is provided to instrumentation and control (I&C) functions during normal operations and for a specified maximum duty cycle following a loss of AC power.
In PSAR Section 8.2.2, Design Bases, Kairos states that the normal power system does not perform any safety-related functions, is not credited for the mitigation of postulated events, and is not credited
with performing safe shutdown functions. Further, Kairos states in PSAR Section 8.2.3, System Evaluation that malfunction of the normal power system will not cause reactor damage or prevent safe reactor shutdown. Section 8.2.3 also states that adequate independence is maintained between the non-safety normal power system and Class 1E Instrumentation and Control System. The I&C system is evaluated in Chapter 7 of this document. In the staffs review of PSAR Chapter 8 and, particularly, Figure 8.1-1, Electrical Configuration Diagram, the staff notes a dedicated connection from the utility to the normal power system.
PDC 17, Electric power systems, requires that electric power systems shall be provided when required to permit functioning of SSCs. PDC 18, Inspection and testing of electric power systems, requires that electric power systems which are safety significant shall be designed to permit appropriate inspection and testing. During an audit, the staff requested clarification on the electrical systems that Kairos stated met PDC 17 and 18. Kairos affirmed the information in Section 8.2, that no electrical systems were required for performing any safety-related function for safe shutdown of the plant or to keep the plant in the safe shutdown condition. The staff finds the PSAR statements that the normal power system is not credited for accident mitigation or safe shutdown, is classified as non-Class 1E or non-safety, no technical specifications for the normal power system are required, and that PDCs 17 and 18 are not applicable since there are no Class 1E electric power systems.
Conclusion The NRC staff finds that the level of detail provided on the normal power system meets the applicable criteria of NUREG-1537, Part 2, Section 8.1, and demonstrates an adequate design basis for a preliminary design. The design bases of the normal electrical power systems for the facility have been reviewed. Because AC power from off-site sources will not be required to perform safe shutdown functions in the preliminary design, the reactor can be safely shut down in the event of a loss or interruption of the normal electrical power system. A more detailed evaluation of information will occur during the review of Hermes final safety analysis report (FSAR), at which time the NRC staff will confirm that the final design conforms to this design basis.
Based on its review, the NRC staff finds that the design of the Hermes normal power system, as described in Hermes PSAR Section 8.2, is sufficient and meets the applicable regulatory requirements and guidance for the issuance of a construction permit in accordance with Title 10, Code of Federal Regulations (10 CFR), Part 50.35. The staff also finds that PDCs 17 and 18 are not applicable since there are no Class 1E electrical power systems.
8.3 Backup Power System Introduction While there are no emergency electrical power systems, Hermes PSAR Section 8.3, Backup Power System (BPS), states the backup power systems design function is to provide AC electrical power to the essential facility loads when the normal AC power supply is not available and includes backup generators and UPS, as well as electrical equipment and circuits used to interconnect the backup generators to the low voltage AC electrical power distribution. The PSAR further states that the facility is equipped with a plug-in connection for use with a portable 480 VAC generator to provide power to essential loads in the event the backup generators are unavailable.
Regulatory Evaluation The applicable regulatory requirements for the evaluation of Hermes are as follows:
10 CFR 50.34, Contents of applications; technical information, paragraph (a), Preliminary safety analysis report, including:
o 10 CFR 50.34(a)(3), which requires The preliminary design of the facility including: (i) The principal design criteria for the facility and (ii) The design bases and the relation of the design bases to the principal design criteria.
o 10 CFR 50.34(a)(4), which requires [a] preliminary analysis and evaluation of the design and performance of structures, systems, and components [SSCs] of the facility; and 10 CFR 50.35, Issuance of construction permits.
10 CFR 50.40, Common standards.
The PDC for the facility SSCs are described in PSAR Section 3.1 and are based on those specified in the NRC-approved Kairos Power Topical Report, KP-TR-003-NP-A. Hermes PSAR, Chapter 3, Table 3.1-3, Principal Design Criteria identifies the PDC 17 and 18 as applicable to electrical power systems.
Technical Evaluation PSAR Section 8.3.1.1, Backup generators, states that the backup generators automatically start in the event of a loss of offsite power and provide power to essential facility loads. Further, Kairos states that there will be at least one redundant generator. In addition, PSAR Section 8.3.1.2, Uninterruptible Power Supplies, states that selected loads are supplied with AC power via UPS and the UPS provides backup power during a loss of normal electrical power. Kairos stated in PSAR Section 8.3.2, Design Bases, that the BPS does not perform any safety-related functions, is not credited for the mitigation of postulated events, and is not credited with performing safe shutdown functions. The BPS, as stated in Section 8.3.3, System Evaluation, is designed according to NFPA 70, National Electric Code 2020, so that postulated failures of SSCs in the system do not preclude a safety-related SSC from performing its safety function.
In the PSAR, Kairos addressed the classification and design attributes of the BPS and the staff finds that PDCs 17 and 18 are not applicable since there are no Class 1E electric power systems.
The NRC staff finds that the level of detail provided on the backup power system satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 8.1, and demonstrates an adequate design basis for a preliminary design. A more detailed evaluation of information will occur during the review of Hermess FSAR, at which time the NRC staff will confirm that the final design conforms to this design basis.
Conclusion Based on its review, the NRC staff finds that the description of the Hermes backup power system, as described in Hermes PSAR Section 8.3, is sufficient and meets the applicable regulatory requirements and guidance for the issuance of a construction permit in accordance with 10 CFR 50.35. The staff also finds that PDCs 17 and 18 are not applicable since there are no Class 1E electrical power systems.
8.4 References Kairos Power LLC. Submittal of the Preliminary Safety Analysis Report for the Kairos Power Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes), Revision 1, September 2022, ADAMS No. ML22272A593.
. Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled, High Temperature Reactor,
KP-TR-003-NP-A. June 12, 2020. ADAMS ML20167A174 National Fire Protection Association (NFPA) 70, National Electrical Code 2020 Nuclear Regulatory Commission (U.S.) (NRC). NUREG-1537, Part 2, "Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors Standard Review Plan and Acceptance Criteria." NRC: Washington, D.C. February 1996. ADAMS Accession No. ML042430048
. Report on General Regulatory Audit for the Hermes Construction Permit Application Review, dated XX, 202X. ADAMS Accession No. MLXXXXXXXXX.